Immunolocalization of the thyrotropin-releasing hormone prohormone in the rat central nervous system.

The distribution of immunoreactive TRH prohormone in the rat central
nervous system was studied by immunocytochemistry using an antiserum
raised against a synthetic decapeptide hypothesized to represent a
portion of the mammalian TRH precursor protein. Reaction product was
identified in several regions of the brain in a distribution typical of
that previously described for the tripeptide. In contrast to TRH,
however, immunoreactive pro-TRH was largely confined to neuronal
perikarya and only rarely seen in axons or axon terminals. In addition,
immunoreactive pro-TRH was present in portions of the telencephalon and
brainstem where TRH has not previously been described in neurons by
immunocytochemistry. These studies indicate that in most regions of the
brain the TRH prohormone is rapidly processed within the cell soma and
not during axonal transport, and raise the possibility that in certain
regions of the brain processing of the prohormone may be to non-TRH
peptides, which may be of biological importance.